Dust and sludge produced as by-product in the individual processes of iron making, steel making, casting, rolling, machining and so forth at ironworks contain a large fraction having a grain size of as fine as several tens of micrometers or smaller, wherein a part of which is recycled as being used for sintering which employs usually iron ore powder as a main raw material.
The microparticulate dust and microparticulate sludge, however, may obstruct gas permeability and fusing performance in the process of sintering, and therefore only a limited amount of use is allowable. They may be used only to as much as several percent even if they were used as being mixed with iron ore powder, and may be recycled only to as much as 10% or around even if the granulation thereof were enhanced typically by mini-pelletizing.
On the other hand, some of the microparticulate dust and microparticulate sludge contain impurities such as zinc, alkali, oils and so forth. These impurities may be causative of various failures in the process of sintering. For this reason, most part of the microparticulate dust and microparticulate sludge with the impurities have not been recycled despite of their large contents of useful elements such as iron, carbon and so forth. For example, zinc contained therein may vaporize and disseminate, contained in the exhaust gas, adhere to a heat-resistance grate, and cause clogging. Alkali contained therein may worsen dust collection efficiency of a dust precipitator, and increase suspended particle concentration. Oils contained therein may be causative of sudden combustion of an electric dust precipitator, so that the amount of use is strictly limited.
On the other hand, there has been proposed a method of sintering using LD converter dust as the main raw material, typically in Patent Document 1. The technique makes use of exothermic effect of metal iron contained in the LD converter dust.
Patent Document 2 proposes updraft sintering (upward suction type) method, by which the LD converter dust is sintered while being removed with zinc (see FIG. 3).
Non-Patent Document 1 proposes, as a technique of consuming a large amount of iron ore particles having a particle size of several hundreds of micrometers, a method of granulating a microparticulate raw material (approximately 60%) and a nucleus material using preliminarily a drum mixer or disk pelletizer.
Similarly, as a technique of using a large amount of microparticulate iron ore, there is also provided a method of mixing 40% of microparticulate raw material to a common raw material for sintering (ore powder 60%), granulating the mixture using a disk pelletizer besides drum mixer to produce pellets of 5 to 10 mm, adding coke fines, and then sintering the pellets coated with coke.
Patent Document 4 proposes, as one technique of enhancing granulation, a vibration kneading granulation process by which a large number of compaction media are housed in a vessel, and allowing microperticulate raw material added with water to granulate in the vessel under an acceleration of circular vibration of 3 to 10 G (G: acceleration of gravity). This technique is reportedly effective when fine ore having a grain size of smaller than 63 μm is granulated to as much as 80% or more.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-248320
[Patent Document 2] Japanese Patent Application Laid-Open No. H10-330851
[Patent Document 3] Japanese Patent Application Laid-Open No. H8-193226
[Patent Document 4] Japanese Patent Application Laid-Open No. H3-166321
[Non-Patent Document 1] “Shoketsu Genryo no Zoryu to sono Yakuwari (Granulation of Raw Material for Sintering and Roles Thereof”, Tetsu-to-Hagane, Vol. 71, No. 10 (1988)